The present invention relates, in general, to an apparatus for overdrilling of buried pipes.
Nothing in the following discussion of the state of the art is to be construed as an admission of prior art.
An overdrilling apparatus is used to clear buried cables and pipelines (hereinafter called “lines”) without excavations and then to renew them. This is realized with the aid of a flushing liquid for example, optionally assisted by cutting and reaming tools, to create a ring channel which surrounds the line and allows the old line to be pulled or pushed out with little friction as well as a new line to be pulled or pushed in.
German Pat. No. DE 195 04 484 C1 describes an overdrilling apparatus which includes a linkage having a forward end for arrangement of a ring-shaped overdrilling head which embraces the old line and includes nozzles for discharge of a flushing liquid, with the nozzles pointing in advance direction. Approximately half of the wall of the ring-shaped overdrilling head has a substantially crescent-shaped cross section for attachment of the linkage which extends to the side of the old line. The flushing liquid migrates via the linkage to nozzles which are arranged in irregular spaced-apart relationship in a ring-shaped manner and have length and jet axes in parallel relationship to the length axis of the overdrilling head. The nozzle jets are intended to flush out the line so long as permitted by the soil consistency and to create hereby in concert with the overdrilling head an annular space which is intended to allow a line exchange with little friction.
However, this is achieved oftentimes only insufficiently because the liquid jets of the nozzles, arranged in the form of a ring at a distance to the old line, cannot reach the line surface, at least not to the extent and with the intensity required for removal of deposits, in view of the parallel disposition of their axes in relation to the length axis of the line and the overdrilling head, respectively. Moreover, in order to reduce the friction between overdrilling head and line, the inner diameter of the overdrilling head of conventional devices exceeds the outer diameter of the line. In this way, an annular gap is created between the overdrilling head and the line, whereby the annular gap has a width which varies, however, locally because the line continuously shifts radially in relation to the overdrilling head under the influence of the soil and the gravitational force acting upon the line. As a result, the width of the annular gap constantly changes locally, i.e. the line and the overdrilling head no longer assume a coaxial relationship. This is accompanied by the risk that tools arranged at the end surface of the overdrilling head can touch and damage the line. Furthermore, soil can migrate into the annular gap between the overdrilling head and the line and may settle there and/or stabilize an unwanted eccentric disposition of the overdrilling head.
It would therefore be desirable and advantageous to provide an improved overdrilling apparatus which obviates prior art shortcomings and constructed to not only center the overdrilling head when clearing an underground line without excavation but also to liberate optionally the surface of the line from adherents.